Thanks for answering that question for me. The S25 was on the the engine that was in the bike when I got it , I think it was a 10D. I have since sourced a 30c which I am restoring but there was no carb. with it. S19's seemed to be very in short supply so i will have to contiue looking for one.One more question if i can. I have been rebuilding the 3 speed for 30c but i cannot find a yoke that does not have stress cracks in it, all 4 peaks on the gearbox yoke's that i have checked all have the same stress cracks in the steel. I wonder has any one else noticed this at all.Richard